The Queensland-based engineer was born in Portsmouth in April 1966, and was later adopted by a local family who had ties to the Queen .
He claims his adopted grandmother, who had worked in the Palace, told him that his real mum and dad were the Prince of Wales and the Duchess of Cornwall.
Charles and Camilla would have been teenagers at the time, decades before they were officially a couple.
Without providing evidence, Simon recently told 7News : "My research has shown that Camilla disappeared off the social scene from August 1965 until June 1966, which is the time that she would have been pregnant with me.
"And in December 1965, Charles was sent off to Australia until after my birth in April 1966."
He also wants Charles and Camilla to submit to a DNA test.
Simon continued: "This is a lengthy legal process and one I'm not giving up. I have taken my case to the Australian High Court, but they referred it back to the Family Court – and that will happen again in the next few months.
"I'm also seeking legal representation in the UK to take my fight abroad as well.
"I'm not interested in doing DNA tests with other distant royals because at the end of the day, I will still need to take it to court. I want this done the right way, before a judge."
During his time in the UK, Simon claims he was taken to various homes to meet with Camilla .
Simon believes he was taken to Broadlands House, a stately home in Hampshire owned by the Mountbatten family – who have family ties to the royals .
The Queen and Prince Philip were pictured in the house's grounds for their diamond wedding anniversary in 2007.
Simon earlier said: "I have very clear memories of both the inside of the house and the grounds.
"I only stayed there for a few hours at a time, but I was there multiple times."
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Simon, who holds British citizenship, made plans to return to the UK in 2012, but both he and his wife were supposedly placed on a "no travel list".
Simon says he later received a formal letter of apology from the Metropolitan Police and was removed from the no-fly list.
The royals have never responded to the allegations.
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